Recirculated exhaust gas (“EGR”) is an important element for both diesel and gasoline engines, particularly engines utilizing intake charge boosting (ex. exhaust driven turbocharger or engine driven supercharger) for both fuel consumption improvements and for reduction in regulated tailpipe exhaust gas emissions.
Typically, the cooling of EGR has been achieved separately from the cooling of the compressed intake charge due to the substantial temperature differential between that of the exhaust gas and the compressed intake charge. EGR is often cooled through a gas-to-liquid charge cooler that utilizes coolant from the engines primary cooling system as the cooling medium. As a result, however, in an engine that has reached normal operating temperatures, the minimum temperature of the EGR may be limited by the temperature of the engine coolant (the typical temperature coolant range may be 90 to 110 degrees C. as set by a thermostat) in the primary cooling system. The cooling of the compressed intake charge is typically achieved through a gas-to-liquid, or more likely a gas-to gas (ex. ambient air) type of heat exchanger. Gas-to gas compressed intake charge cooling is more often found in today's engine applications. However, the utilization of a gas-to-liquid compressed intake charge cooler has the advantage of improved system transient response and has been receiving increased attention as downsized, boosted internal combustion engines are considered as a key solution to improving fuel economy and engine-out emissions.